Positive electrode active material for non-aqueous electrolyte secondary cell and cell using the same

Abstract

There is provided a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a composite oxide represented by the general formula (1): (Li1-xMx)a(Co1-yMy)bOc where lithium and cobalt are partly replaced with element M in the crystal structure of LiCoOc, wherein element M is at least one selected from the group consisting of Al, Cu, Zn, Mg, Ca, Ba and Sr, and 0.02≦x+y≦0.15, 0.90≦a / b≦1.10, and 1.8≦c≦2.2 are satisfied.

Description

TECHNICAL FIELD[0001]The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery for use in, for example, personal digital assistants, portable electronic appliances and home-use power storage devices as well as two-wheeled motor vehicles, electric vehicles and hybrid electric vehicles, each of which employs a motor as the power source.BACKGROUND ART[0002]Non-aqueous electrolyte secondary batteries, which have been recently used in various fields, have high electromotive force and high energy density. As the positive electrode active material for non-aqueous electrolyte secondary batteries, lithium cobaltate (LiCoO2) is mainly used. This substance has a high oxidation-reduction potential of 4 V or higher with respect to lithium.[0003]The above positive electrode active material repeatedly expands and contracts during charge / discharge. In such an occasion, the positive electrode ...

AI Technical Summary

Benefits of technology

[0008]The present invention solves the foregoing problems and it has an object of improving a positive electrode active material to suppress an increase in battery thickness due to repeated charge / discharge cycles, thereby retaining the discharge capacity and thermal stability of a battery.

Problems solved by technology

Non-aqueous electrolyte secondary batteries, which have been recently used in various fields, have high electromotive force and high energy density.

In such an occasion, the positive electrode active material undergoes distortion, structural destruction and pulverization, resulting in a problem of a decrease in the discharge capacity during charge / discharge cycles.

In the case of square batteries or laminated batteries, the problem of an increase in battery thickness needs to be addressed because the cases thereof have poor strength.

However, also in this case, the battery thickness gradually increases owing to repeated charge / discharge cycles.

It is considered that repeated charge / discharge cycles increase distortion between these layers, resulting in an expansion of the crystal lattice.

As described above, since conventional positive electrode active materials undergo distortion, structural destruction and pulverization due to repeated charge / discharge cycles, they have a disadvantage of increasing the battery thickness and decreasing the discharge capacity.

As a result, although the batteries have high thermal stability during the initial charge / discharge period, they have another disadvantage that the structure of the positive electrode active materials become unstable to cause an insufficient thermal stability after repeated charge / discharge cycles.

Images